OK the current set up is unusual, so unusual temperatures are perhaps
not too unexpected.
But I notice the long term Met Office forecast suggests westerlies at
the end of next week, accompanied by "average or a little below
average" temperatures. I've noticed that's been very much the norm in
July and August (less in June) - standard westerly types have tended
to be on the low side rather than the high side of average - even when
the sun has been shining. This contrasts with recent summers, which
have seen westerly types with temps generally slightly above normal in
summer. Has the air just not had a chance to warm up properly this
year?

There have been very few periods, winter or summer, in recent years
with such a sustained period with a tendency for temperatures to be
below average. The only other one I can think of is Feb-Mar 2006,
which at least was the right season....

A warm September and Octber followed by a cold winter is appropriate
payback for this summer, I feel :-)

Nick